1. Technical Field
This invention relates generally to machinery for producing finished wood products and more specifically to a device including a rotating cutter assembly for notching pallet stringers.
2. Background of the Invention
Pallets are used in a variety of industries as a relatively low cost means for stacking, storing and handling raw materials and manufactured and bulk goods. A pallet typically includes series of top deckboards which are nailed to a the upper surface of a series of substantially parallel and equally spaced stringers, typically three, two side or end stringers and a center stringer. Several lower deckboards are then nailed to the lower surface of the stringers to provide the required rigidity to the pallet assembly. Both the upper deck boards and the lower deckboards are nailed to the stringers so that the longitudinal axes of the deckboards are substantially perpendicular to the longitudinal axes of the stringers.
The stringers may be fabricated from dimensional lumber which is sized and oriented to allow adequate spacing between the upper and lower deckboards of the pallet to permit the tine of a fork lift or other lift mechanism to be inserted between the upper and lower deckboards. For example, if the stringer is manufactured from two inch by four inch lumber, (two-by-four), the stringer would be oriented so that the upper and lower deckboards would be nailed to the side having the two inch dimension, allowing a spacing between the upper and lower deckboards of four inches.
A two-way pallet permits access by the lifting mechanism from the front or rear of the pallet. The tines of the lifting mechanism are insertable between and more or less parallel to the stringers. A four-way pallet permits access by the lifting mechanism from the front, rear or sides of the pallet. The tines of the lifting mechanism may be inserted between the stringers or in the alternative, the tines of the lifting mechanism may be inserted through a pair of notches through the face of each stringer. Each stringer has a corresponding pair of notches allowing the tines to be inserted from either side of the pallet and under substantially the full width of the pallet.
A four-way pallet is constructed by notching the stringers with a notching machine prior to assembly of the pallet. The industry's standard dimensions for notches are one and one-half inches high by nine inches wide. Following notching, the stringers are placed in a jig or an automatic pallet manufacturing machine where the top and bottom deckboards are nailed to the stringers with an automatic air driven nail gun. A considerable number of stringers are broken at the reduced cross section of the notch during the manufacturing process due to a combination of reduced strength of the stringer and the force of the nail gun piston that is required to drive and set the nails with a single stroke. It would, therefore, be desirable from a cost standpoint to notch the stringer after the pallet has been assembled.
Heretofore, the step of notching the stringers must occur prior to assembly and nailing of the pallet. The notching operation requires the stringers to be hand loaded onto a feed chain mechanism to convey them across the notch cutters to form the notch. Stringers are stacked face to face to provide backing to the two-by-four being cut to hold tearout to a minimum. After the notching operation the stringers are restacked and delivered to a pallet assembly area.
Stringers are next placed in a jig or a pallet assembly machine so the top and bottom deckboards can be nailed in place. Automatic nail machines must operate at very high pressures to insure that each nail is completely set in one stroke. Some stringers will break when a nail is driven into the two-by-four at the reduced cross section of the notch thus requiring the pallet to be removed from the automatic assembly and stacking machine, often retained for repair or salvage. Considerable labor and materials must be expended to replace the broken stringers.
Presently, notching is achieved using a rotating cutter assembly having a plurality of blades each having a plurality of cutting teeth mounted about the periphery of the blade. The plurality of blades are mounted on a horizontal shaft driven by a motor so that the blades rotate in a vertical plane. This configuration has not been demonstrated as being suitable for notch cutting assembled pallets as the vertically rotating blades have a distinct tendency to cause tear-outs at the backside of the notch upon completion of the cut. Tear-outs further reduce the strength of the stringer by creating additional stress risers in the already weakened region of the notch. This propensity to cause tear-outs can be reduced by providing a backing for each stringer being cut. This is done by stacking the stringers in the notch cutter, hence the prospect of notch cutting assembled pallets has not been practical to date.
Therefore, it would be desirable to provide an alternate method and device for pallet manufacture which would eliminate the requirement to notch cut stringers prior to pallet assembly, thereby reducing stringer breakage and overall pallet assembly costs.